Catalytic destruction of halogenated hydrocarbons

ABSTRACT

The destruction of chlorinated hydrocarbons, such as carbon tetrachloride, over lanthanide-based solid catalysts in the presence of steam has been investigated between 200 and 350° C. Ln 2 O 3 /AL 2 O 3  (e.g. Ln=La, Nd, Ce and Pr) show a very high catalytic hydrolysis activity. The destruction capacity gradually increases with increasing temperature and reaches a maximum value of 42.3.10 6  ppm·h −1  at 350° C. for a 10 wt % Ln 2 O 3 /AL 2 O 3  catalyst This destruction capacity could be maintained for a least 48 hours. The catalyst activity is also function of the type of lanthanide oxide; i.e., La≈Nd&gt;Ce≈Pr. The process is based on a delicate equilibrium between destructive adsorption of CCI 4  onto the lanthanide oxide and the dechlorination of the formed lanthanide chloride with steam. Steam being responsible for the in situ regeneration of the catalytic active phase.

FIELD OF INVENTION

The present invention relates to catalytic methods and compositions forhydrolytic destruction of halogenated hydrocarbons. In addition theinvention provides methods to control the reaction products obtained inthe catalytic process, this control allowing the conversion ofhalogenated hydrocarbons towards valuable chemicals.

BACKGROUND OF THE INVENTION

Although they are proven to be highly toxic and carcinogenic,chlorinated hydrocarbons (CHC's) are still widely used in themanufacturing of many chemical compounds, such as herbicides, fungicidesand pharmaceuticals [1]. CHC's are also applied in dry cleaningprocesses, in degreasing operations and as organic solvents [2]. As aconsequence, CHC's are found in the flue gases of many industrialinstallations. In the present context industry is defined broadly, itencompasses combustion processes, from power plants to municipal wasteincineration, and also processes where volatile chlorinated hydrocarbonsare made (both deliberately and as by-products), or where they are used.The compounds that are important for this activity and are thought tohave important fluxes from industry are: carbon tetrachloride (CCl₄),methyl chloride (CH₃Cl), dichloromethane (CH₂Cl₂ or methylene chloride),trichloromethane (CHCl₃ or chloroform), trichloroethene (CCl₂═CHCl ortrichloroethylene) and tetrachloroethene (CCl₂═CCl₂ orperchloroethylene), chlorobenzene, chlorotoluene as well as derivativesthereof.

The current method to remove CHC's is thermal incineration attemperatures higher than 1300° C. These high temperatures are requiredto avoid the formation of dioxins and polychlorobiphenyls (PCB's) [3].Because of the high incineration temperatures and consequently, the highcosts, scientists are forced to look for other but cheaper alternativesthat are not harmful to the environment [4].

A first alternative process is the catalytic oxidation of CHC's attemperatures between 300° C. and 550° C. over supported noble metalcatalysts (e.g. Pt, Pd and Au) [5-9]. The essential drawback here is thedeactivation of the catalyst by the decomposition products including Cl₂and HCl [10]. Another disadvantage is the formation of volatileoxychlorides, which can condense and block the installation in thecolder parts of the reactor. The formation of these by-products can(partially) be solved by adding small amounts of steam to the CHC'sfeed. In contrast, it has been stated that supported transition metaloxide catalysts are resistant to these kinds of deactivation [11]. Amongthese types of oxides Cr₂O₃ seems to be the most promising catalyst forthe total oxidation of CHC's [12-15]. Frequently used supports areAl₂O₃, TiO₂ and SiO₂[16]. Other classes of materials are zeolites (e.g.H—Y and H-ZSM-5 zeolites), perovskites (e.g. LaCoO₃ and LaMnO₃) andpillared clays [17-21].

A second alternative for incineration is hydrodechlorination in which aCHC is transformed in the presence of hydrogen into the correspondingalkane and HCl [22,23]. Commonly used catalysts are Pd and Pt on varioussupports [24,25]. Ni/SiO₂ catalysts also seem to possess a high activity[26]. Although this technique has economic and environmental advantages,Including the re-use of the reaction products and the elimination ofhazardous by-products (e.g. Cl₂ and COCl₂), it is not used very often.The main reason is the very fast deactivation of the catalyst material.This deactivation is probably due to the interaction between HCl and thecatalyst and to coke formation caused by oligomers formed on the acidsites of the catalyst.

A third alternative for incineration was provided by Weckhuysen e.a. (J.Phys. Chem B, 1998, 102, 3773-3778). They have studied the destructiveadsorption of carbon tetrachloride on alkaline earth metal oxides, morespecifically BaO, SrO, CaO and MgO. They concluded that alkaline earthmetal oxides are active materials for the destructive adsorption ofcarbon tetrachloride in the absence of O₂. The destruction activityparallels the basicity of the alkaline earth metal oxide; i.e., theactivity towards CCl₄ decreases in the order: BaO>SrO>CaO>MgO. Carbontetrachloride destruction was accompanied by the formation of chlorides(BaCl₂; SrCl2, CaCl₂ and MgCl₂ in the case of BaO, SrO, CaO and MgO,respectively). They observed that the resulting barium chloride isrecycable by dissolving the solid in water, followed by precipitationand heating in oxygen. The biggest disadvantage of this techniquehowever is that it is a stoechiometric and not a catalytic process. Thismeans that, once the metal oxide is converted to the correspondingchloride, the activity of the system falls back to almost undetectabledestruction levels.

The U.S. Pat. No. 4,561,969 provides a process for the removal of thehalogen moiety from halogenated hydrocarbon feedstock. The homogenousprocess described in this patent depends on the use of sulfuric acid anda lanthanide oxide, the latter being required to break the chlorine ionfrom the hydrocarbon in order to form a chlorosulfonic acid. The oxidesare regenerated by bubbling O₂ through the depleted H₂SO₄ solution.

The present invention provides a solution to the aforesaid problems byoffering methods and catalytic compositions for hydrolytic destructionof halogenated hydrocarbons in a heterogeneous process. In addition theinvention provides methods to control the reaction products obtained inthe catalytic process, this control allowing the conversion ofchlorinated hydrocarbons towards valuable chemicals.

SUMMARY OF THE INVENTION

The present invention is related to compositions and methods useful fortreating gas streams containing halogenated hydrocarbons.

One embodiment of this invention relates to a method for hydrolyticdestruction of halogenated hydrocarbons, comprising the steps of: (a)providing a gas stream comprising halogenated hydrocarbons; and (b)contacting the gas stream with an effective amount of a compositioncomprising a lanthanide oxide or a mixture of lanthanide oxides. In thisembodiment the destruction of the halogenated hydrocarbons isaccompanied by the formation of halogenated metal oxides.

In another embodiment this invention relates to a method for thecatalytic hydrolytic destruction of halogenated hydrocarbons, comprisingthe steps of: (a) providing a gas stream comprising halogenatedhydrocarbons; and (b) contacting the gas stream with an effective amountof a composition comprising a lanthanide oxide or a mixture oflanthanide oxides in the presence of steam.

In another embodiment this invention relates to a method for thecatalytic hydrolytic destruction of halogenated hydrocarbons, comprisingthe steps of: (a) providing a gas stream comprising halogenatedhydrocarbons; and (b) contacting the gas stream with an effective amountof a composition comprising a lanthanide oxide or a mixture oflanthanide oxides in the presence of steam. Said lanthanide oxide ormixture of lanthanide oxides being supported on alumina, ceria, titania,silica, silica-alumina, manganese oxide, zirconia, zeolites or mixturesor composites thereof. Nevertheless, it was demonstrated that thehighest destruction conversions were obtained when the lanthanide oxidewas supported on alumina. Therefore, in a more preferred embodiment acomposition comprising a lanthanide oxide or mixture of lanthanideoxides, which is supported by alumina, is used for the catalyticdestruction of halogenated hydrocarbons according to the presentinvention.

A further embodiment relates to a catalyst for hydrolytic destruction ofgaseous halogenated hydrocarbons comprising a lanthanide oxide or amixture of lanthanide oxides as an active phase. In a more preferredembodiment said lanthanide oxide or mixture of lanthanide oxides issupported on alumina, ceria, titania, silica, silica-alumina, manganeseoxide, zirconia, zeolites or mixtures or composites thereof. In an evenmore preferred embodiment said lanthanide oxide or mixture of lanthanideoxides is supported on alumina. In another preferred embodiment theamount of the lanthanide oxide or mixture of lanthanide oxides of asteam regenerated catalytic preparation exceeds 5% of the total weightof the dry weight of said catalytic preparation.

Different parameters modulate the destruction capacity of the method ofthe present invention. In first instance, it was demonstrated that thedestruction capacity gradually increases with increasing temperaturebetween 200 and 350° C. for a 10 wt % La₂O₃/Al₂O₃ catalyst. In secondinstance it was demonstrated that the catalyst activity can becontrolled by the type of lanthanide oxide; i.e., the catalytic functionof La≈Nd>Ce≈Pr. In third instance it was shown that the catalyticdestruction activity differed between supported or unsupportedcatalysts. Therefore, a person skilled in the art will understand thatthe manipulation of said parameters amongst others would lead todifferent reaction products of the catalytic hydrolysis process. Moreparticularly, the parameters can be set in order to obtain reactionproducts that can be used as precursors of valuable chemicals. In apreferred embodiment the parameters were set in order to realise anincomplete destruction of CH₂Cl₂ and CHCl₃ and the selective formationof methyl chloride (CH₃Cl). Methyl chloride is employed in thepreparation of methanol, dimethyl ether, light olefins, such ethylene,propylene and butenes and higher hydrocarbons, including gasolines. Thisembodiment of the invention can be beneficially employed in industrialprocesses using significant amounts CH₂Cl₂, such as the production ofcleaning solvents and paint removers or in processes using significantamounts of CHCl₃, such as stain removers, teflon andChlorofluorocarbons.

A person skilled in the art understands that the catalytic destructionof halogenated hydrocarbons using the catalytic composition of thepresent invention is based on a chemical equilibrium. The reaction withthe halogenated hydrocarbons generates lanthanide oxide halogens andeventually lanthanide halogens, while on the other hand steam acts onthe lanthanide oxide halogens and lanthanide halogens to regenerate thelanthanide oxides in the catalytic composition. Given this equilibrium,it is clear that the catalytic composition of the present invention canbe prepared using lanthanide oxides, lanthanide oxide halogens orlanthanide halogens or using mixtures thereof.

DESCRIPTION OF THE DRAWINGS

FIG. 1: Conversion of carbon tetrachloride over a 10 wt % La₂O₃/Al₂O₃catalyst as a function of the reaction temperature.

FIG. 2: Conversion of carbon tetrachloride over 10 wt % supportedlanthanide oxide catalysts at 350° C.

FIG. 3: Influence of the presence of steam on the conversion of CCl₄over a 10 wt % La₂O₃/Al₂O₃ catalyst at 350° C.

FIG. 4: Comparison of the catalytic destruction activity of supportedand unsupported lanthanide oxide catalysts at 350° C.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is based on the finding that rare earth metaloxides, such as La₂O₃ and CeO₂, allow the destructive adsorption ofhalogenated hydrocarbons, such as carbon tetrachloride, in the absenceof oxygen (Weckhuysen e.a., Physical Chemistry Chemical Physics, 1999,1(13): 3157-3162). This destruction of the halogenated hydrocarbons wasaccompanied by the formation of metal oxide chlorides and as such it wasa stoechiometric process, as was previously observed for the alkalineearth metal oxides. However, surprisingly it was possible to create anefficient catalytic system by adding steam to the reactor. The presenceof the steam allows converting the formed metal oxide chlorides againinto metal oxides in one single process.

A first aspect of present invention is a process for the catalyticdestruction of halogenated hydrocarbons, comprising the steps of: (a)providing a gas stream comprising halogenated hydrocarbons; and (b)contacting the gas stream with an effective amount of a compositioncomprising a lanthanide oxide or a mixture of lanthanide oxides.Preferably this process is carried out under conditions allowing theregeneration of the lanthanide oxides following their reaction with thehalogenated hydrocarbons, which can be achieved by the presence of steamin said gas stream. In a preferred embodiment the composition comprisinga lanthanide oxide or a mixture of lanthanide oxides, is a solidcatalyst supported by a suitable substrate and more preferably thesubstrate is a high surface alumina. The term high surface area is meantto describe surface areas comprising at least 80 m²/g, typically from 80to 300 m²/g. In yet another preferred embodiment said compositioncomprises a lanthanide oxide or a mixture of lanthanide oxides havingthe general formula Ln₂O₃. The lanthanide (Ln) in this general formulabeing selected out of the group of Lanthanum, Cerium, Praseodymium,Neodymium, Promethium, Samarium, Europium, Gadolinium, Terbium,Dysprosium, Holmium, Erbium, Thulium, Ytterbium and Lutetium and morepreferably the lanthanide oxide catalyst is selected from the group ofcompounds consisting of La₂O₃, Nd₂O₃, Pr₂O₃ and Ce₂O₃.

Preferably the halogenated hydrocarbons which are destructed by theprocess of present invention are fluorine hydrocarbons and mostpreferably chlorine hydrocarbons.

A second aspect of present invention is a catalytic process ofconverting chlorinated hydrocarbons in a flue gas into the reactionproducts CO₂ and HCl comprising flowing said halogenated hydrocarbonsover a lanthanide oxide catalyst further comprising measuring theconcentration of chlorinated hydrocabons in said flue gas from reactionsite and accordingly adjusting the gas flow, temperature and steamsupply at the reaction site to monitor the catalytic performance. Thisprocess may further comprise measuring unwanted reaction products, suchas dioxins and/or polychlorobiphenyls, in said flue gases from reactionsite and adjusting the reaction temperature accordingly to monitor theformation of unwanted reaction products of the destruction of saidchlorinated or fluorinated hydrocarbons. In a preferred embodiment thisdechlorination process comprises the use of lanthanide oxide catalystsof the group La₂O₃/Al₂O₃, Pr₂O₃/Al₂O₃, Nd₂O₃/Al₂O₃ and Ce₂O₃/Al₂O₃ andthe destruction of chlorinated hydrocarbons occurs under steam and at atemperature below 350° C. or at a temperature of about 350° C. Mostpreferably the supported lanthanide oxide catalysts is a La₂O₃/Al₂O₃catalyst and preferably the amount of La₂O₃ is at least 5 wt % of thetotal dry weight of the catalyst composition, for example 10 wt %.

A third aspects of the present invention relates to the use of saidprocess for the destruction of halogenated hydrocarbons in order toobtain reaction products that can be used as precursors of valuablechemicals. Indeed, different parameters modulate the destructioncapacity of the method of the present invention. In first instance, itwas demonstrated that the destruction capacity gradually increases withincreasing temperature between 200 and 350° C. for a 10 wt % La₂O₃/Al₂O₃catalyst. In second instance it was demonstrated that the catalystactivity can be controlled by the type of lanthanide oxide; i.e., thecatalytic function of La≈Nd>Ce≈Pr. In third instance, it was shown thatthe catalytic destruction activity differed between supported orunsupported catalysts. So the manipulation of said parameters, amongstothers, leads to different reaction products of the catalytic hydrolysisprocess. More particularly, the parameters can be set in order to obtainreaction products that can be used as precursors of valuable chemicals.In a preferred embodiment the parameters were set in order to realise anincomplete destruction of CH₂Cl₂ and CHCl₃ and the selective formationof methyl chloride (CH₃Cl). Methyl chloride is employed in thepreparation of methanol, dimethyl ether, light olefins, such ethylene,propylene and butenes and higher hydrocarbons, including gasolines. Thisembodiment of the invention can be beneficially employed in industrialprocesses using significant amounts CH₂Cl₂, such as the production ofcleaning solvents and paint removers or in processes generatingsignificant amounts of CHCl₃, such as stain removers, teflon andChlorofluorocarbons.

A fourth aspect of the present is a process for the stripping ofhalogenated hydrocarbons dissolved or suspended in water or othersolvents. Said solvents can either be organic or inorganic. A typicalexample is the stripping of the waste waters of a production plant usingor producing halogenated hydrocarbons. In a preferred embodiment thisstripping process uses the catalytic, hydrolitic destruction ofhalogenated and comprises the following steps (a) chasing thehalogenated hydrocarbons out of the liquid phase, for example by heatingthe liquid phase or by flushing the liquid phase with a suitable gas,(b) contacting the gas stream containing said chased halogenatedhydrocarbons with an effective amount of said catalytic lanthanideoxide-comprising composition, preferably in the presence of steam.

The preparation of the support materials for the catalysts of thisinvention may be prepared by means well known to those of ordinary skillin the art and include physical mixtures, coagulation, co-precipitationor impregnation. The techniques for preparing the materials bycoagulation and co-precipitation may be found, for example, in U.S. Pat.No. 4,085,193. Typically support materials prepared by the methodsdescribed are in the form of a fine powder. The support material can beused in powdered form. Alternatively, the support material in powderedform can be subsequently formed into larger particles and particulateshapes. The catalytic material may be applied to the support materialprior to forming the support material into a particulate shape, oralternatively after the support is shaped into particulate form. Thesupport material may be shaped into particulate or pellet form, such asextrudates, spheres and tablets, using methods well known in the art.For example, catalyzed support powder can be combined with a binder suchas a clay and rolled in a disk pelletizing apparatus to give catalystspheres. The amount of binder can vary considerably but for convenienceis present from about 10 to about 30 weight percent.

The catalytic material can be dispersed onto the support materials bymeans well known in the art. A preferred method is impregnation, whereinthe support material in particulate or powder form is impregnated with asolution containing a soluble compound of the catalytic metal or metals.The solution may be an aqueous solution, one using an organic solvent,or a mixture of the two. An aqueous solution is preferred. The solublecompounds of the metal ion(s) should transform to the metal oxides uponheating in air at elevated temperatures and/or in the presence of steam.

The catalyst of the invention may be used in any configuration, shape orsize, which exposes it to the gas to be treated. For example, thesupported catalyst can be conveniently employed in particulate form orthe supported catalyst can be deposited as a coating onto a solidmonolithic substrate. In some applications when the particulate form isused it is desirable to provide a screen-like barrier that permits theflow of the gas stream but inhibits the movement of the solidparticulates from one catalyst bed to the other.

In circumstances in which less mass is desirable or in which movement oragitation of particles of catalyst may result in attrition, dusting andresulting loss of dispersed metals, or undue increase in pressure dropacross the particles due to high gas flows, a monolithic substrate ispreferred. In the employment of a monolithic substrate, it is usuallymost convenient to employ the supported catalyst as a thin film orcoating deposited on the inert substrate material which thereby providesthe structural support for the catalyst. The inert substrate materialcan be any refractory material such as ceramic or metallic materials. Itis desirable that the substrate material be unreactive with the catalystand not be degraded by the gas to which it is exposed. For the treatmentof gases containing halogenated organics, ceramic materials arepreferred.

The monolithic substrate can best be utilized in any rigid unitaryconfiguration, which provides a plurality of pores or channels extendingin the direction of gas flow. It is preferred that the configuration bea honeycomb configuration. The honeycomb structure can be usedadvantageously in either unitary form, or as an arrangement of multiplemodules. The honeycomb structure is usually oriented such that gas flowis generally in the same direction as the cells or channels of thehoneycomb structure. For a more detailed discussion of monolithicstructures, refer to U.S. Pat. No. 3,785,998 and U.S. Pat. No.3,767,453. In a preferred embodiment, the honeycomb substrate has about50 to about 600 cells per square inch of cross-sectional area. In anespecially preferred embodiment, the honeycomb has about 100 to about400 cells per square inch.

If a monolithic form is desired, each layer of catalyst of thisinvention can be deposited sequentially onto the monolithic honeycombcarrier by conventional means. For example, a slurry can be prepared bymeans known in the art such as combining the appropriate amounts of thesupported catalyst of this invention in powder form, with water. Theresultant slurry is typically ball-milled for about 8 to 18 hours toform a usable slurry. Other types of mills such as impact mills can beused to reduce the milling time to about 1-4 hours. The slurry is thenapplied as a thin film or coating onto the monolithic carrier by meanswell known in the art. Optionally, an adhesion aid such as alumina,silica, zirconium silicate, aluminum silicates or zirconium acetate canbe added in the form of an aqueous slurry or solution. A common methodinvolves dipping the monolithic carrier into said slurry, blowing outthe excess slurry, drying and calcining in air at a temperature of about450° C. to about 600° C. for about 1 to about 4 hours. This procedurecan be repeated until the desired amount of catalyst of this inventionis deposited on said monolithic honeycomb substrate.

An alternative method of preparation is to disperse the catalytic metalor metals and such other optional components on a monolithic substratecarrier which previously has been coated with only uncatalyzed supportmaterial by the above procedure. The compounds of catalytic metal, whichcan be used and the methods of dispersion are the same as describedabove. After one or more of these compounds have been dispersed onto thesupport material coated substrate, the coated substrate is dried andcalcined at a temperature of about 400° C. to about 600° C. for a timeof about 1 to 6 hours. If other components are desired, they may beimpregnated simultaneously or individually in any order.

The present invention is based on the discovery that lanthanide-basedsolid catalysts have a high catalytic hydrolysis activity in thedestruction of halogenated hydrocarbons such as carbon tetrachloride, inthe presence of steam and in a proper temperature range of 200 and 350°C. The following is a demonstration of these findings by illustrativeembodiments. The terminology used herein is for the purpose ofdescribing particular embodiments only, and is not intended to limit thescope of the present invention.

EXAMPLE 1 Preparation of the Solid Catalyst Composition

The solid catalysts were prepared via the incipient wetness impregnationtechnique with aqueous solutions of the lanthanide compounds in theiracetate form (Aldrich, >99.9%). Al₂O₃ (Condea) with a specific surfaceof 220 m²/g, was used as support and contacted with the appropriateamount of impregnation solution. The impregnated samples were dried in afurnace at 100° C. for one hour. This operation was repeated until thedesired lanthanide oxide loading was obtained. The catalysts weregranulated and the fraction of 0.25-0.50 mm was used for catalyticexperiments.

EXAMPLE 2 Testing of the Catalytic Composition in a Catalytic Process

Catalytic tests were performed in a fixed-bed reactor at atmosphericpressure. The reactor consists of a quartz tube loaded with 1 g ofcatalyst. The catalyst was first heated in the reactor tube overnight inan oxygen flow of 10 ml·min⁻¹ at 45° C. and then subjected at 250° C.,300° C. or 350° C. to a stream of He loaded with CCl₄ (VEL, p.a.). TheCCl₄ loading in the He stream could be controlled by adjusting thetemperature of the CCl₄ saturator. The total He flow was set at 8ml·min⁻¹ resulting in a maximum CCl₄ loading of 47000 ppm (v/v). Thespace velocity (GHSV) was maintained at 800 h⁻¹. The gas flows weremeasured and controlled by mass flow controllers. Water was added to thereactor at a rate of 0.02 ml·min⁻¹ via a dosimeter and evaporated whenin contact with the reactor walls and bed. The condensate was trapped inan impinger at room temperature at the end of the reactor tube. Theremaining gases were guided to a gas chromatograph (HP 4890D with FIDdetector and methanator) equipped with a packed Hayesep Q CP column(80-100 mesh, 3 m length). The condensate was regularly analysed using agas chromatograph of Perkin-Elmer Autosys equipped with a FID-detectorand a CP-Sil 5CB column (inner diameter, 0.32 mm; film thickness, 0.25μm; length, 40 m).

EXAMPLE 3 Preparation and Constituents of the Catalyst Composition

Experiments regarding the formulation and mode of preparation of thecatalyst composition lead to the following observations:

-   1) Preferably aqueous solutions of the compounds in their acetate    form are used. Catalyst compositions that were impregnated with the    precursors in the nitrate form, obtained a 20% lower CCl₄ conversion    than catalysts impregnated with acetate solutions.-   2) Al₂O₃ is a preferred support, experiments performed with other    supports than Al₂O₃ (such as SiO₂ and TiO₂) revealed systematically    lower destruction conversions.

EXAMPLE 4 Destruction activity of La₂O₃/Al₂O₃, catalysts for CCl₄

FIG. 1 shows the destruction activity of a 10 wt % La₂O₃/Al₂O₃ catalystas a function of the reaction temperature for a CCl₄ loading of 47000ppm (v/v) in the presence of steam. The catalytic conversions weremeasured after 6 hours time-on-stream. It is clear that the conversionis around 0% at 200° C. but gradually increases with increasing reactiontemperature up to a value of 100% at 350° C. The Al₂O₃ support materialpossess at these temperatures a short term activity of 45%, while thecatalytic activity of La₂O₃ is around 60%. No other products than HCland CO₂ were found in the effluent gas and in the collected condensate.This indicates the total hydrolysis of CCl₄ with steam to HCl and CO₂.

EXAMPLE 5 Comparison of La₃O₃/Al₂O₃ Catalysts for CCl₄ with OtherCatalytic Systems

Table I compares the destruction capacities of the 10 wt % La₂O₃/Al₂O₃catalyst with other catalytic systems in the open and patent literatureoperating in the same temperature range (0-350° C.). It is clear thatthe 10 wt % La₂O₃/Al₂O₃ catalyst is three times more active than thebest performing catalyst, namely Pt, Pd or Rh/TiO₂ catalysts,(Allied-Signal, Morristown, N.J.) reported up to now in the open andpatent literature. In another series of experiments we have studied thestability of the 10 wt % La₂O₃/Al₂O₃ catalyst and observed that thetotal conversion of CCl₄ could be maintained for at least 48 hours.

EXAMPLE 6 Comparison of Different of Lanthanide Oxide-Based Catalysts

FIG. 2 compares the conversion of CCl₄ over a series of 10 wt %Ln₂O₃/Al₂O₃ materials after 6 hours time-on-stream for a CCl₄ loading of47000 ppm (v/v). Two catalysts show 100% conversion, namely La₂O₃/Al₂O₃and Nd₂O₃/Al₂O₃, while Ce₂O₃/Al₂O₃ and Pr₂O₃/Al₂O₃ have a destructionactivity of about 85%. Thus, the destruction activity increases in theorder: Pr≈Ce<La≈Nd.

EXAMPLE 7 Influence of Steam on the Catalytic Performance of LanthanideOxide-Based Catalysts

In another experiment we have studied the Influence of steam on thecatalytic performance of a 10 wt % La₂O₃/Al₂O₃ catalyst for a CCl₄loading of 40000 ppm (v/v) measured at 350° C. The catalytic results aresummarised in FIG. 3. The experiment started with a period in which nosteam was added to the reaction system and water was only added to thereaction mixture after about 16 hours time-on-stream. FIG. 3 shows thatinitially the conversion was 100% but this destruction activitygradually decreases with increasing time-on-stream. After about 14 hoursthe conversion was only 22%. Addition of steam dramatically increasesthe conversion up to a value of 90%. This experiment points towards thecrucial role of steam for maintaining the catalyst activity.

EXAMPLE 8 Incomplete Destruction CCl₄ and the Selective Formation ofCH₃Cl

It was found that the catalytic hydrolysis process over some halogenatedhydrocarbons, such as CH₂Cl₂, can lead to different reaction products.This is illustrated in FIG. 4. FIG. 4 compares the catalytic destructionactivity of supported and unsupported lanthanide oxide catalysts at 350°C. For the unsupported catalysts the only product is CO₂/CO and HCl(complete destruction to the final products). In contrast, the supportedcatalysts form CH₃Cl and CO besides HCl. This means that it is possibleto realise an incomplete destruction process and the selective formationof CH₃Cl by changing the catalyst composition. This opens a new routetowards the conversion of chlorinated hydrocarbons towards valuablechemicals, more specifically alkanes and alkenes. Indeed, it is known inopen literature that acid zeolites, such as H-ZSM-5 and SAPO-34, areable to convert CH₃Cl into e.g. ethylene.

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[28] Petrosius, S. C.; Drago, R. S.; Young, V.; Grunewald, G. C.Low-Temperature Decomposition of Some Halogenated Hydrocarbons UsingMetal Oxide/Porous Carbon Catalysts. Journal of the American ChemicalSociety 1993, 115, 6131-6137. TABLE 1 Overview of catalytic materialsexisting in the literature for the destruction of CCl₄ in thetemperature range 0-350° C. Loading GHSV Temperature Destructioncapacity Catalyst CCl₄ (ppm) (h⁻¹) (° C.) (10⁶ ppm/h) Reference LaMnO₃  500   6000 350 2.4 18 LaCoO₃   500   6000 350 0.6 18 Co-Y  1 000  1367 350 1.4 27 Cr-Y  1 000   1367 350 1.4 27 Carbon 60 000    50 2501.4 28 Cr₂O₃/Al₂O₃  1 000 15 000 350 5.3 4 Pt, Pd or Rh/TiO₂  1 000 15000 350 15 4 (Allied-Signal, Morristown, NJ) La₂O₃/Al₂O₃ 47 000   800250 12.7 This work La₂O₃/Al₂O₃ 47 000   800 300 22.4 This workLa₂O₃/Al₂O₃ 47 000   800 350 42.3 This work

1. A catalytic process for the destruction of halogenated hydrocarbonsin a gas stream, comprising the hydrolysis of the halogenatedhydrocarbons by flowing said halogenated hydrocarbons over a lanthanideoxide catalyst, or a mixture of lanthanide oxides, in the presence ofsteam at a temperature higher than 200° C. and lower than or about 350°C. 2-19. cancelled.
 20. The catalytic process according to claim 1,wherein the temperature varies between about 250° C. and about 350° C.21. The catalytic process according to claim 1, wherein water is addedto said gas stream.
 22. The catalytic process of claim 1, wherein saidlanthanide oxide catalyst, or mixture of lanthanide oxides, is a solidcatalyst supported by a suitable substrate.
 23. The catalytic process ofclaim 1, wherein said lanthanide oxide catalyst, or mixture oflanthanide oxides, is a solid catalyst supported by a suitable substrateand wherein said substrate is selected from the group consisting ofalumina, titania, silica, silica-alumina, manganese oxide, zirconia,zeolites and mixtures thereof.
 24. The catalytic process of claim 1,wherein said lanthanide oxide catalyst, or mixture of lanthanide oxides,is a solid catalyst supported by a suitable substrate and wherein saidsubstrate is alumina with a surface area from 80 to 300 m²/g.
 25. Thecatalytic process of claim 1, wherein said lanthanide oxide catalyst hasthe general formula of Ln₂O₃.
 26. The catalytic process of claim 1,wherein said lanthanide oxide catalyst is selected from the group ofcompounds consisting of La₂O₃, Nd₂O₃, Pr₂O₃, and Ce₂O₃.
 27. Thecatalytic process of claim 1, wherein the destruction of halogenatedhydrocarbons is catalysed by an Al₂O₃ supported lanthanide oxidecatalyst.
 28. The catalytic process of claim 1, wherein said processconverts chlorinated hydrocarbons in a flue gas into the reactionproducts CO₂ and HCl, further comprising measuring the concentration ofchlorinated hydrocarbons in said flue gas from reaction site andaccordingly adjusting the gas flow, temperature and steam supply at thereaction site to monitor the catalytic performance.
 29. The catalyticprocess of claim 28, further comprising measuring unwanted reactionproducts, such as dioxins and/or polychlorobiphenyls, in said flue gasesfrom reaction site and adjusting the reaction temperature to monitor theformation of said unwanted reaction products or the destruction of saidchlorinated hydrocarbons.
 30. The catalytic process of claim 1, whereinsaid lanthanide oxide catalyst, or mixture of lanthanide oxides, is asolid catalyst supported by a suitable substrate and wherein saidsupported lanthanide oxide catalyst is selected from the groupconsisting of La₂O₃/Al₂O₃, Pr₂O₃/Al₂O₃, Nd₂O₃/Al₂O₃, and Ce₂O₃/Al₂O₃.31. The catalytic process of claim 1, wherein said lanthanide oxidecatalyst, or mixture of lanthanide oxides, is a solid catalyst supportedby a suitable substrate and wherein said supported lanthanide oxidecatalyst is a La₂O₃/Al₂O₃ catalyst and the amount of La₂O₃ is at least 5wt % of the total dry weight of the catalyst composition.